DISEASE CHARACTERISTICS: Histologically or cytologically confirmed adenocarcinoma of the colon or rectum Metastatic/recurrent disease not amenable to potentially curative therapy (e.g., inoperable metastatic disease) Documented sequential disease progression (by CT scan or MRI) after 2 prior chemotherapy regimens for metastatic/recurrent disease At least 1 unidimensionally measurable lesion At least 20 mm by conventional CT scan or MRI OR At least 10 mm by spiral CT scan Must have received prior fluorouracil (or capecitabine) and leucovorin calcium with or without irinotecan as first-line therapy and irinotecan with or without fluorouracil (or capecitabine) and leucovorin calcium as second-line therapy for metastatic disease